Soft start control method, primary side control device, secondary side feedback device and switching power supply

Abstract

The invention discloses a soft start control method, a primary side control device, a secondary side feedback device and a switching power supply. The soft start control method comprises the following steps: outputting a second feedback control signal after the steps of output voltage detection, comparative judgment processing, modulation, isolation processing, demodulation and first blanking processing; then, entering a soft start control execution step, and detecting whether the duration time of a second feedback control signal appearing for the first time is greater than a first set value or not in real time in a soft start control stage: if so, entering closed-loop control; if not, a fault detection step is started, and the fault detection step comprises the steps that whether the duration time that a second feedback control signal appearing for the first time is equal to 1 is larger than a second set value or not is detected, and if the second set value is larger than the first set value, the following control logic is executed according to the detection result: if not, output short-circuit protection is started; and if yes, stopping executing the first blanking processing and the fault detection step, and entering closed-loop control. The reliability of the switching power supply can be improved.

Description

Technical Field

[0001] The present invention relates to the field of power supply control, and in particular to a soft start control method, a primary side control device, a secondary side feedback device and a switching power supply. Background Art

[0002] Traditional isolated DC-DC power supply chips, such as Figure 1 As shown. The primary side of the chip mainly includes a demodulation unit, an oscillator circuit, an output short circuit detection and protection execution unit, and a drive circuit. The secondary side of the chip mainly includes a rectifier circuit, an output voltage detection unit, a reference voltage circuit, a comparison output unit, and a modulation unit. In addition, the chip also contains a transformer for energy transmission and an isolation capacitor for signal transmission.

[0003] The startup process of the isolated power supply is as follows: (1) The primary chip is powered by an external power supply, and the primary energy is transferred to the secondary side through a transformer, and then the secondary side is powered after rectification. Before the primary chip is powered on, the secondary side has no power; (2) After the primary voltage is greater than the undervoltage protection threshold, the primary side starts soft start, and the secondary voltage gradually increases. When the secondary voltage is greater than the secondary undervoltage point, the secondary side starts to work normally. At this time, the voltage VDIV after resistor voltage division is less than the reference voltage VREF, and the output PWM=0 signal is transmitted to the primary side through the digital isolator; (3) The primary side short-circuit protection control circuit detects the feedback control signal FB=0, the primary side maintains soft start, and the secondary side voltage continues to be powered on; (4) As the secondary voltage rises, when the voltage VDIV after resistor voltage division is greater than the reference voltage VREF, that is, when the secondary output voltage VISO is greater than the rated voltage, the comparison output PWM=1; the primary side short-circuit protection control circuit detects that the FB=1 width is greater than the set value, closes the primary side soft start, and the switching power supply enters closed-loop control; and under the closed-loop control of the feedback control signal FB, the output voltage of the switching power supply reaches stability.

[0004] In (4), the soft start and closed-loop control state are switched by detecting the width of FB=1. The detected FB signal is a narrow pulse with a fixed pulse width, and its anti-interference ability is weak, resulting in the following problems:

[0005] (1) In a switching power supply that transmits energy at high frequencies, noise interference can cause internal voltage fluctuations, resulting in abnormal output of the secondary comparator.

[0006] (2) The modulation and demodulation unit is prone to mismodulation or misinterpretation under noise interference, resulting in erroneous narrow pulses;

[0007] (3) Under noise interference, the primary side soft start narrow pulse detection circuit cannot accurately measure the narrow pulse time and cannot close the soft start circuit in time, resulting in an overshoot of the output voltage of the switching power supply. Summary of the invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide a soft start control method, a primary side control device, a secondary side feedback device and a switching power supply, which at least solve one of the technical problems existing in the prior art to a certain extent.

[0009] The present invention aims to improve the anti-interference ability of the signal transmission process between the primary side control device and the secondary side feedback device during the soft start process, and ensure that the output voltage of the switching power supply will not overshoot when the soft start detection fails through fault detection technology, thereby ensuring the reliability and efficiency of the power switch power supply.

[0010] As a first aspect of the present invention, the technical solution of the embodiment of the soft start control method provided is as follows:

[0011] A soft start control method is applied to a switching power supply, wherein the switching power supply includes a transformer, wherein the soft start control method includes:

[0012] An output voltage detection step, converting the AC signal output by the secondary side of the transformer into a DC voltage, and obtaining a first voltage signal VDIV representing the magnitude of the DC voltage;

[0013] A comparison and judgment processing step, comparing the first voltage signal with a reference voltage to generate a first PWM signal;

[0014] A modulation step of modulating the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON;

[0015] an isolation processing step, isolating the first modulation signal ISOP into a first isolation signal VIOP, and isolating the second modulation signal ISON into a second isolation signal VION;

[0016] A demodulation step, demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal;

[0017] A first blanking processing step, performing blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then outputting a second feedback control signal FB_LEB;

[0018] The soft start control execution step is to detect in real time during the soft start control stage whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than the first set value:

[0019] If yes, turn off the soft start control and enter closed-loop control;

[0020] If not, start the fault detection steps, including:

[0021] It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than a second set value, and the second set value is greater than the first set value, and the following control logic is executed according to the detection result:

[0022] If not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is restarted after a third set time;

[0023] If yes, the soft start control is turned off, the first blanking processing step and the fault detection step are stopped, and the closed-loop control enters a stable working stage.

[0024] Preferably, the modulation step modulates the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON by an OOK modulation method.

[0025] Furthermore, the comparison and judgment processing step further judges whether the first PWM signal is 0, and outputs the second PWM signal according to the judgment result. Specifically, if the first PWM signal is 0, the first PWM signal is directly used as the second PWM signal; otherwise, the second blanking processing step is performed, and the first PWM signal is blanked to eliminate the hidden danger of false triggering and then used as the second PWM signal;

[0026] The modulation step modulates the second PWM signal into a first modulation signal ISOP and a second modulation signal ISON.

[0027] Furthermore, the control signal of the soft start control is a duty cycle and a frequency that change incrementally at the same time.

[0028] As a second aspect of the present invention, the technical solution of the embodiment of the primary side control device provided is as follows:

[0029] A primary side control device is applied to a switching power supply, wherein the switching power supply includes a transformer, wherein the primary side control device includes:

[0030] A demodulation unit, used for demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal;

[0031] A first blanking processing unit, configured to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output a second feedback control signal FB_LEB;

[0032] A soft start control execution unit and a fault detection unit, wherein the soft start control execution unit is used to detect in real time during the soft start control stage whether the duration of the second feedback control signal FB_LEB equal to 1 for the first time is greater than a first set value:

[0033] If yes, turn off the soft start control and enter closed-loop control;

[0034] If not, starting the fault detection unit includes:

[0035] It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than a second set value, and the second set value is greater than the first set value, and the following control logic is executed according to the detection result:

[0036] If not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is restarted after a third set time;

[0037] If yes, turn off the soft start control, turn off the first blanking processing unit and the fault detection unit, and enter the stable working stage of closed-loop control;

[0038] Wherein: the first isolation signal VIOP is generated by the first modulation signal ISOP generated by the secondary feedback device and isolated and processed by the isolation processing device; the second isolation signal VION is generated by the second modulation signal ISON generated by the secondary feedback device and isolated and processed by the isolation processing device;

[0039] The secondary side feedback device generates the first modulation signal ISOP and the second modulation signal ISON through the following units:

[0040] An output voltage detection unit, which converts the AC signal output by the secondary side of the transformer into a DC voltage, and obtains a first voltage signal VDIV representing the magnitude of the DC voltage;

[0041] A comparison output unit, which compares the first voltage signal with a reference voltage and outputs a first PWM signal;

[0042] The modulation unit modulates the first PWM signal into the first modulation signal ISOP and the second modulation signal ISON.

[0043] As a third aspect of the present invention, the technical solution of the embodiment of the secondary side feedback device provided is as follows:

[0044] A secondary side feedback device is applied to a switching power supply, wherein the switching power supply includes a transformer, wherein the secondary side feedback device includes:

[0045] An output voltage detection unit, used for converting the AC signal outputted by the secondary side of the transformer into a DC voltage, and obtaining a first voltage signal VDIV representing the magnitude of the DC voltage;

[0046] A comparison and judgment processing unit, used for comparing the first voltage signal with a reference voltage to generate a first PWM signal;

[0047] A modulation unit, configured to modulate the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON;

[0048] Wherein: the first modulation signal ISOP is isolated and processed by the isolation processing unit to be the first isolation signal VIOP, and the second modulation signal ISON is isolated and processed by the isolation processing unit to be the second isolation signal VION; the primary side control device performs soft start control through the following units according to the first isolation signal VIOP and the second isolation signal VION:

[0049] a demodulation unit, configured to demodulate the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal;

[0050] A first blanking processing unit, configured to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output a second feedback control signal FB_LEB;

[0051] A soft start control execution unit and a fault detection unit, wherein the soft start control execution unit is used to detect in real time during the soft start control stage whether the duration of the second feedback control signal FB_LEB equal to 1 for the first time is greater than a first set value:

[0052] If yes, turn off the soft start control and enter closed-loop control;

[0053] If not, starting the fault detection unit includes:

[0054] It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than a second set value, and the second set value is greater than the first set value, and the following control logic is executed according to the detection result:

[0055] If not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is restarted after a third set time;

[0056] If yes, the soft start control is turned off, the first blanking processing unit and the fault detection unit are turned off, and the closed-loop control enters a stable working stage.

[0057] Furthermore, the secondary side feedback device further includes a second blanking processing unit;

[0058] The comparison and judgment processing step is also used to judge whether the first PWM signal is 0, and output the second PWM signal according to the judgment result. Specifically: if the first PWM signal is 0, directly use the first PWM signal as the second PWM signal; otherwise, start the second blanking processing unit, and use the second blanking processing unit to blank the first PWM signal to eliminate the risk of false triggering and then use it as the second PWM signal;

[0059] The modulation step modulates the second PWM signal into a first modulation signal ISOP and a second modulation signal ISON.

[0060] As a fourth aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0061] A switching power supply, comprising a transformer, wherein: the switching power supply further comprises the primary side control device and the isolation processing device as described in any one of the second aspects above, and the secondary side feedback device as described in any one of the third aspects above.

[0062] Compared with the prior art, the present invention can effectively improve the controllability and stability during the soft start process, avoid noise interference leading to soft start control failure of the switching power supply, and thus cause output voltage overshoot. The beneficial effects are analyzed in detail as follows:

[0063] In the embodiment of the present invention, after blanking processing is performed on the first feedback control signal FB to eliminate the hidden danger of false triggering, the second feedback control signal FB_LEB is output, and then the second feedback control signal FB_LEB is used to perform soft start control. In the soft start control stage, it is detected in real time whether the time when the second feedback control signal FB_LEB appears for the first time to be equal to 1 is greater than the first set value. If not, the fault detection unit is started to detect whether the time when the second feedback control signal FB_LEB appears for the first time to be equal to 1 is greater than the second set value (the second set value is greater than the first set value): if not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is performed again after the third set time; if yes, the soft start control is turned off, the first blanking processing step and the fault detection step are stopped, and the switching power supply is forced to switch to the closed-loop control mode, which can avoid abnormal switching of the soft start mode due to internal noise interference, causing output voltage overshoot, and improve the reliability and safety of the switching power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a soft start architecture of a switching power supply in the prior art;

[0065] Figure 2A soft start architecture according to an embodiment of the present invention;

[0066] Figure 3 is a flow chart of a first soft start control method according to a first embodiment of the present invention;

[0067] Figure 4 is a flow chart of a second soft start control method according to the first embodiment of the present invention;

[0068] Figure 5 The switching power supply of the fourth embodiment of the present invention adopts Figure 2 SYS_OUT waveform change diagram of the soft start architecture under the change of duty cycle and frequency during the soft start process;

[0069] Figure 6 The switching power supply of the fourth embodiment of the present invention adopts Figure 2 Detailed waveforms of the soft-start architecture during the switching process between primary-side soft-start control and closed-loop control. DETAILED DESCRIPTION

[0070] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0071] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0072] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0073] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0074] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0075] Figure 2 A soft start architecture according to an embodiment of the present invention includes a primary side control device, an isolation processing device and a secondary side feedback device, wherein:

[0076] The primary side control device includes a demodulation unit, a first blanking processing unit, a fault detection unit, an oscillator circuit, a soft start control execution unit and a driving circuit; the primary side control device receives the secondary side feedback control signal, and controls the switching power supply to switch between the soft start mode and the closed loop control mode through the soft start control execution unit. The demodulation unit is used to demodulate the PWM modulation signal of the secondary side into a feedback control signal FB, and the first blanking processing unit will ignore all possible trigger signals during the first set time window. It is known to those skilled in the art that the first blanking processing unit will shield the feedback control signal FB input therein during this time, ensuring that the soft start control and fault detection (if any) are performed only when the signal output by the demodulation unit is stable, thereby effectively avoiding the premature termination of the soft start process due to signal fluctuations and improving the stability of the switching power supply.

[0077] When the fault detection unit detects the duration of the first occurrence of the feedback control signal FB_LEB=1 during the soft start phase, since the second setting value of the fault detection unit is greater than the first setting value of the soft start control execution unit, the soft start control execution unit is not enabled before the first occurrence of FB_LEB=1, and the soft start control execution unit normally collects the feedback control signal FB to perform soft start mode and closed loop control mode detection and control. When the duration of the first occurrence of FB_LEB=1 is greater than the first setting value, the primary side soft start ends and enters the stable working stage, which is controlled by FB_LEB; if the duration of the feedback control signal FB_LEB=1 is greater than the second setting value, it is determined that the function of the soft start control execution unit is abnormal, and the fault detection unit enables the soft start control execution unit, forcing the switching power supply to switch to the closed loop control mode, which can avoid the abnormal switching of the soft start mode due to internal noise interference, causing the output voltage overshoot, and improve the reliability and safety of the switching power supply; if the duration of the first occurrence of FB_LEB=1 is less than the second setting value, it is determined that the output of the switching power supply is short-circuited, and the primary side drive is immediately turned off, and the soft start is restarted after the third setting time.

[0078] The secondary feedback device includes a rectifier circuit, an output voltage detection circuit, a reference voltage circuit, a comparison output unit, a second blanking processing unit and a modulation unit; the voltage division VDIV of the secondary output voltage VISO is compared with the reference voltage VREF to output a PWM signal, and the second blanking processing unit will ignore all possible trigger signals during the second set time window to ensure that the corresponding signal modulation is performed only when the PWM signal is stable, effectively avoiding the transmission of erroneous signals to the primary side due to signal fluctuations, and improving the accuracy of signal transmission. The PWM_LEB signal output by the second blanking processing unit is modulated into a high-frequency carrier signal and transmitted to the primary side through a digital isolator.

[0079] First embodiment

[0080] This embodiment provides a soft start control method, which is applied to a switching power supply, wherein the switching power supply includes a transformer, Figure 3 is a flow chart of a first soft start control method according to a first embodiment of the present invention, Figure 4 This is a flow chart of the second soft start control method of the first embodiment of the present invention. Figure 3 and Figure 4 , and combined with Figure 2 , where the soft start control method includes:

[0081] An output voltage detection step, converting the AC signal output by the secondary side of the transformer into a DC voltage, and obtaining a first voltage signal VDIV representing the magnitude of the DC voltage;

[0082] A comparison and judgment processing step, comparing the first voltage signal VDIV with the reference voltage VREF to generate a first PWM signal;

[0083] A modulation step of modulating the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON;

[0084] An isolation processing step of isolating the first modulation signal ISOP into a first isolation signal VIOP and isolating the second modulation signal ISON into a second isolation signal VION;

[0085] A demodulation step, demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal;

[0086] The first blanking processing step is to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output the second feedback control signal FB_LEB. In the primary side soft start stage, VDIV<VREF, FB is always 0. Due to internal interference, FB may jump to 1, so the first blanking processing step needs to be set;

[0087] The soft start control execution step is to detect in real time during the soft start control stage whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than the first set value:

[0088] If yes, turn off the soft start control and enter closed-loop control;

[0089] If not, start the fault detection steps, including:

[0090] It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than the second set value, and the second set value is greater than the first set value. The following control logic is executed according to the detection result:

[0091] If not, it is determined that the switching power supply output is short-circuited, and the primary side drive is immediately turned off. After the third set time, the soft start is restarted;

[0092] If yes, the soft start control is turned off, the first blanking processing step and the fault detection step are stopped, and the closed-loop control enters a stable working stage.

[0093] In this embodiment, the first feedback control signal FB is blanked to eliminate the hidden danger of false triggering, and then the second feedback control signal FB_LEB is output. Then, the second feedback control signal FB_LEB is used to perform soft start control. In the soft start control stage, it is detected in real time whether the time during which the second feedback control signal FB_LEB appears to be equal to 1 for the first time is greater than the first set value. If not, the fault detection unit is started to detect whether the time during which the second feedback control signal FB_LEB appears to be equal to 1 for the first time is greater than the second set value (the second set value is greater than the first set value): if not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is performed again after the third set time; if yes, the soft start control is turned off, the first blanking processing step and the fault detection step are stopped, and the switching power supply is forced to switch to the closed-loop control mode, which can avoid abnormal switching of the soft start mode due to internal noise interference, causing output voltage overshoot, thereby improving the reliability and safety of the switching power supply.

[0094] As a specific implementation manner, the modulation step modulates the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON by using an OOK modulation method.

[0095] In the primary soft start phase, VDIV < VREF, PWM is always = 0. Due to internal interference, the PWM signal may jump to 1. The PWM signal can be blanked to generate the PWM_LEB signal. For a specific implementation method, see Figure 3 , wherein the comparison and judgment processing step further judges whether the first PWM signal is 0, and outputs the second PWM signal according to the judgment result, specifically: if the first PWM signal is 0, directly use the first PWM signal as the second PWM signal, otherwise execute the second blanking processing step, in which the first PWM signal is blanked to eliminate the hidden danger of false triggering and then used as the second PWM signal; the modulation step modulates the second PWM signal into the first modulation signal ISOP and the second modulation signal ISON.

[0096] As a specific implementation method, the control signal of the soft start control is a duty cycle and a frequency that change incrementally at the same time, thereby effectively reducing the startup EMI.

[0097] Second embodiment

[0098] This embodiment provides a primary side control device, which is applied to a switching power supply, wherein the switching power supply includes a transformer, wherein the primary side control device includes:

[0099] A demodulation unit, used for demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal;

[0100] A first blanking processing unit, configured to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output a second feedback control signal FB_LEB;

[0101] The soft start control execution unit and the fault detection unit are used to detect in real time during the soft start control stage whether the duration of the second feedback control signal FB_LEB equal to 1 for the first time is greater than the first set value:

[0102] If yes, turn off the soft start control and enter closed-loop control;

[0103] If not, start the fault detection unit, including:

[0104] It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than the second set value, and the second set value is greater than the first set value. The following control logic is executed according to the detection result:

[0105] If not, it is determined that the switching power supply output is short-circuited, and the primary side drive is immediately turned off. After the third set time, the soft start is restarted;

[0106] If yes, turn off the soft start control, turn off the first blanking processing unit and the fault detection unit, and enter the stable working stage of the closed-loop control;

[0107] Wherein: the first isolated signal VIOP is generated by the first modulation signal ISOP generated by the secondary feedback device and isolated by the isolation processing device; the second isolated signal VION is generated by the second modulation signal ISON generated by the secondary feedback device and isolated by the isolation processing device;

[0108] The secondary side feedback device generates the first modulation signal ISOP and the second modulation signal ISON through the following units:

[0109] The output voltage detection unit converts the AC signal output by the secondary side of the transformer into a DC voltage to obtain a first voltage signal VDIV representing the magnitude of the DC voltage;

[0110] A comparison output unit, which compares the first voltage signal with a reference voltage and outputs a PWM signal;

[0111] The modulation unit modulates the PWM signal into a first modulation signal ISOP and a second modulation signal ISON.

[0112] The technical means adopted by the control device of this embodiment correspond to and are consistent with the control method of the first embodiment, and have the same beneficial effects, so they will not be described in detail.

[0113] In addition, the preferred technical means or further improved means of each step in the control method of the first embodiment can be extended to the corresponding units of this embodiment, and this embodiment will not describe them one by one.

[0114] Third embodiment

[0115] This embodiment provides a secondary side feedback device, which is applied to a switching power supply, wherein the switching power supply includes a transformer, wherein the secondary side feedback device includes:

[0116] An output voltage detection unit, used to convert the AC signal output by the secondary side of the transformer into a DC voltage, and obtain a first voltage signal VDIV representing the magnitude of the DC voltage;

[0117] A comparison and judgment processing unit, used for comparing the first voltage signal with a reference voltage to generate a first PWM signal;

[0118] A modulation unit, configured to modulate the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON;

[0119] Wherein: the first modulation signal ISOP is isolated and processed by the isolation processing unit to be the first isolation signal VIOP, and the second modulation signal ISON is isolated and processed by the isolation processing unit to be the second isolation signal VION; the primary side control device performs soft start control through the following units according to the first isolation signal VIOP and the second isolation signal VION:

[0120] A demodulation unit, used for demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal;

[0121] A first blanking processing unit, configured to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output a second feedback control signal FB_LEB;

[0122] The soft start control execution unit and the fault detection unit are used to detect in real time during the soft start control stage whether the duration of the second feedback control signal FB_LEB equal to 1 for the first time is greater than the first set value:

[0123] If yes, turn off the soft start control and enter closed-loop control;

[0124] If not, start the fault detection unit, including:

[0125] It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than the second set value, and the second set value is greater than the first set value. The following control logic is executed according to the detection result:

[0126] If not, it is determined that the switching power supply output is short-circuited, and the primary side drive is immediately turned off. After the third set time, the soft start is restarted;

[0127] If yes, the soft start control is turned off, the first blanking processing unit and the fault detection unit are turned off, and the closed-loop control enters a stable working stage.

[0128] The technical means adopted by the control device of this embodiment correspond to and are consistent with the control method of the first embodiment, and have the same beneficial effects, so they will not be described in detail.

[0129] As an improvement of this embodiment, the secondary side feedback device further includes a second blanking processing unit;

[0130] The comparison and judgment processing step is also used to judge whether the first PWM signal is 0, and output the second PWM signal according to the judgment result. Specifically: if the first PWM signal is 0, directly use the first PWM signal as the second PWM signal; otherwise, start the second blanking processing unit, and use the first PWM signal as the second PWM signal after blanking the first PWM signal to eliminate the hidden danger of false triggering by the second blanking processing unit;

[0131] The modulation step modulates the second PWM signal into a first modulation signal ISOP and a second modulation signal ISON.

[0132] The preferred technical means or further improved means in each step of the control method in the first embodiment can be extended to the corresponding units of this embodiment, and will not be described one by one in this embodiment.

[0133] Fourth embodiment

[0134] This embodiment provides a switching power supply, which includes a transformer, wherein: the switching power supply also includes any one of the primary side control devices and isolation processing devices in the second embodiment and any one of the secondary side feedback devices in the third embodiment.

[0135] The switching power supply of this embodiment can control the switching of primary soft start control and closed-loop control when the fault detection unit is enabled, ensuring that the output voltage of the switching power supply will not overshoot when the soft start detection fails, thereby ensuring the reliability and efficiency of the switching power supply.

[0136] Figure 5 FIG. 1 is a diagram showing the waveform change of SYS_OUT under the change of duty cycle and frequency during the soft start process of the switching power supply of the fourth embodiment of the present invention using the soft start 2 architecture of FIG. Figure 5 , including the following process:

[0137] After power-on, the soft-start control circuit generates a square wave signal with a duty cycle of 10% and a frequency of 0.75MHz, which lasts for 1ms;

[0138] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 20% and a frequency of 1.5MHz, which lasts for 1ms;

[0139] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 30% and a frequency of 2.3MHz, which lasts for 1ms;

[0140] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 40% and a frequency of 3MHz, which lasts for 1ms;

[0141] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 50% and a frequency of 3.76MHz, which lasts for 1ms;

[0142] If during this period, the voltage division VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 60% and a frequency of 4.6MHz, which lasts for 1ms;

[0143] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 70% and a frequency of 5.5MHz, which lasts for 1ms;

[0144] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 80% and a frequency of 6MHz, which lasts for 1ms;

[0145] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 90% and a frequency of 6.67MHz, which lasts for 1ms;

[0146] If during this period, the voltage divider VDIV of the secondary side VISO voltage is not greater than VREF, the soft start control circuit generates a square wave signal with a duty cycle of 100% and lasts for 51ms;

[0147] If during this period, the voltage division VDIV of the secondary voltage VISO is not greater than VREF, it is considered that the secondary chip is short-circuited or overloaded. At this time, the soft start control circuit outputs 0, and the switching power supply enters the protection stage, which lasts for 60ms before restarting the soft start. The soft start gradually adjusts the duty cycle and frequency, gradually increases the power output to the target value, and can significantly reduce the input surge current at the startup moment, while controlling EMI within an acceptable range.

[0148] Figure 6 The switching power supply of the fourth embodiment of the present invention adopts Figure 2 For detailed waveforms of the soft start architecture during the soft start process, see Figure 6 , the PWM signal output after the voltage division VDIV of the secondary output voltage VISO is compared with the reference voltage VREF passes through the second blanking processing unit, and all possible trigger signals are ignored during the second set time window of the second blanking processing unit. It is known to those skilled in the art that the second blanking processing unit will shield the PWM signal input therein during this time, which can effectively prevent the transmission of erroneous signals to the primary side due to signal fluctuations, thereby improving the accuracy of signal transmission. The PWM signal generates a PWM_LEB signal after passing through the second blanking processing unit, and the PWM_LEB signal is modulated into a high-frequency carrier signal and transmitted to the primary side through a digital isolator. The primary demodulation unit demodulates the high-frequency carrier signal into a feedback control signal FB, and generates a feedback control signal FB_LEB after passing through the first blanking processing unit, and ignores all possible trigger signals during the first set time window of the first blanking processing unit, ensuring that the corresponding soft start control operation is performed only when the demodulated signal is stable, effectively avoiding the output of erroneous signals due to signal fluctuations, so that the soft start control execution unit recognizes that the soft start process is over, resulting in the early end of the soft start, and the output voltage VISO of the switching power supply is low, which cannot maintain the normal operation of the chip. The soft start control execution unit detects the time width of the FB_LEB signal and switches between the soft start mode and the closed-loop control mode. When the second feedback control signal FB_LEB that appears for the first time is equal to 1 and lasts for a time greater than the second set value, it is determined that the soft start control execution unit has failed, and DET_EN becomes a low level to forcibly turn off the soft start. The switching power supply enters the closed-loop control stage to avoid overshoot of the switching power supply output voltage, which affects the reliability and life of the sensitive circuits inside the chip switching power supply.

[0149] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limitations of the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A soft start control method, applied to a switching power supply, the switching power supply comprising a transformer, characterized in that: The soft start control method comprises: An output voltage detection step, converting the AC signal output by the secondary side of the transformer into a DC voltage, and obtaining a first voltage signal VDIV representing the magnitude of the DC voltage; A comparison and judgment processing step, comparing the first voltage signal with a reference voltage to generate a first PWM signal; A modulation step of modulating the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON; an isolation processing step, isolating the first modulation signal ISOP into a first isolation signal VIOP, and isolating the second modulation signal ISON into a second isolation signal VION; A demodulation step, demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal; A first blanking processing step, performing blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then outputting a second feedback control signal FB_LEB; The soft start control execution step is to detect in real time during the soft start control stage whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than the first set value: If yes, turn off the soft start control and enter closed-loop control; If not, start the fault detection steps, including: It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than a second set value, and the second set value is greater than the first set value, and the following control logic is executed according to the detection result: If not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is restarted after a third set time; If yes, the soft start control is turned off, the first blanking processing step and the fault detection step are stopped, and the closed-loop control enters a stable working stage.

2. The soft start control method according to claim 1, characterized in that: The modulation step modulates the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON by an OOK modulation method.

3. The soft start control method according to claim 1, characterized in that: The comparison and judgment processing step further judges whether the first PWM signal is 0, and outputs the second PWM signal according to the judgment result. Specifically, if the first PWM signal is 0, the first PWM signal is directly used as the second PWM signal; otherwise, the second blanking processing step is performed, and the first PWM signal is blanked to eliminate the hidden danger of false triggering and then used as the second PWM signal; The modulation step modulates the second PWM signal into a first modulation signal ISOP and a second modulation signal ISON.

4. The soft start control method according to any one of claims 1 to 3, characterized in that: The control signal of the soft start control is a duty cycle and a frequency that change incrementally at the same time.

5. A primary side control device, applied to a switching power supply, the switching power supply comprising a transformer, characterized in that: The primary side control device comprises: A demodulation unit, used for demodulating the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal; A first blanking processing unit, configured to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output a second feedback control signal FB_LEB; A soft start control execution unit and a fault detection unit, wherein the soft start control execution unit is used to detect in real time during the soft start control stage whether the duration of the second feedback control signal FB_LEB equal to 1 for the first time is greater than a first set value: If yes, turn off the soft start control and enter closed-loop control; If not, starting the fault detection unit includes: It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than a second set value, and the second set value is greater than the first set value, and the following control logic is executed according to the detection result: If not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is restarted after a third set time; If yes, turn off the soft start control, turn off the first blanking processing unit and the fault detection unit, and enter the stable working stage of closed-loop control; Wherein: the first isolation signal VIOP is generated by the first modulation signal ISOP generated by the secondary feedback device and isolated and processed by the isolation processing device; the second isolation signal VION is generated by the second modulation signal ISON generated by the secondary feedback device and isolated and processed by the isolation processing device; The secondary side feedback device generates the first modulation signal ISOP and the second modulation signal ISON through the following units: An output voltage rectification detection unit converts the AC signal outputted by the secondary side of the transformer into a DC voltage, and obtains a first voltage signal VDIV representing the magnitude of the DC voltage; A comparison output unit, which compares the first voltage signal with a reference voltage and outputs a first PWM signal; The modulation unit modulates the first PWM signal into the first modulation signal ISOP and the second modulation signal ISON.

6. A secondary side feedback device, applied to a switching power supply, the switching power supply comprising a transformer, characterized in that: The secondary side feedback device comprises: An output voltage detection unit, used for converting the AC signal outputted by the secondary side of the transformer into a DC voltage, and obtaining a first voltage signal VDIV representing the magnitude of the DC voltage; A comparison and judgment processing unit, used for comparing the first voltage signal with a reference voltage to generate a first PWM signal; A modulation unit, configured to modulate the first PWM signal into a first modulation signal ISOP and a second modulation signal ISON; Wherein: the first modulation signal ISOP is isolated and processed by the isolation processing unit to be the first isolation signal VIOP, and the second modulation signal ISON is isolated and processed by the isolation processing unit to be the second isolation signal VION; the primary side control device performs soft start control through the following units according to the first isolation signal VIOP and the second isolation signal VION: a demodulation unit, configured to demodulate the first isolation signal VIOP and the second isolation signal VION into a first feedback control signal FB, wherein the first feedback control signal FB is a narrow pulse signal; A first blanking processing unit, configured to perform blanking processing on the first feedback control signal FB to eliminate the hidden danger of false triggering and then output a second feedback control signal FB_LEB; A soft start control execution unit and a fault detection unit, wherein the soft start control execution unit is used to detect in real time during the soft start control stage whether the duration of the second feedback control signal FB_LEB equal to 1 for the first time is greater than a first set value: If yes, turn off the soft start control and enter closed-loop control; If not, starting the fault detection unit includes: It is detected whether the duration of the first occurrence of the second feedback control signal FB_LEB being equal to 1 is greater than a second set value, and the second set value is greater than the first set value, and the following control logic is executed according to the detection result: If not, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the soft start is restarted after a third set time; If yes, the soft start control is turned off, the first blanking processing unit and the fault detection unit are turned off, and the closed-loop control enters a stable working stage.

7. The secondary side feedback device according to claim 6, characterized in that: The secondary side feedback device further includes a second blanking processing unit; The comparison and judgment processing step is also used to judge whether the first PWM signal is 0, and output the second PWM signal according to the judgment result. Specifically: if the first PWM signal is 0, directly use the first PWM signal as the second PWM signal; otherwise, start the second blanking processing unit, and use the second blanking processing unit to blank the first PWM signal to eliminate the risk of false triggering and then use it as the second PWM signal; The modulation step modulates the second PWM signal into a first modulation signal ISOP and a second modulation signal ISON.

8. A switching power supply, comprising a transformer, characterized in that: The switching power supply further comprises the primary side control device and the isolation processing device as claimed in claim 5 and the secondary side feedback device as claimed in any one of claims 6 to 7.

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